For purposes of this disclosure, the anatomy of a bone of a human or mammal can be divided into three principal segments: (1) the outer cortical bone that provides a rigid outer structure and weight bearing capabilities of the bone; (2) cancellous bone tissue disposed between the cortical bone and the intramedullary (IM) canal; and (3) the IM canal that passes axially through the cortical bone and cancellous bone tissue. Cancellous bone is substantially weaker than cortical bone. The boundary between the cancellous bone and the outer cortical bone structure is often referred to as the cortical wall.
Certain bone fractures are repaired surgically by clearing a cavity in the IM canal of the fractured bone that traverses the fracture site and installing a filler material and/or other structures in the cavity. Surgical instruments are available for forming such cavities in vertebrae. For example, some instruments include an expandable body or balloon for forming a cavity in the cancellous bone tissue of vertebrae. The expandable body or balloon compresses the cancellous bone to form the cavity. The cavity receives the filler material, which provides interior structural support for cortical bone while the cortical bone heals. Because such devices are not intended to cut bone, at least a small cavity must be cut or otherwise formed in the cancellous bone in a separate procedure in order to initially insert the balloon-like device.
It is frequently desirable to form a larger cavity in an IM canal and cancellous bone than can be formed with devices designed to compress and/or displace cancellous bone or material disposed in the IM canal, rather than cutting and removing such material. However, the concept of cutting and removing cancellous bone without damaging the cortical wall or cortical bone structure is problematic. Specifically, the diameters of IM canals and cortical walls are not constant, but highly irregular and non-circular. The IM canal and cortical wall often have oblong profiles that vary in dimension and geometry not only from individual to individual, but also along the length of a bone axis. As a result, drilling cancellous bone with a conventional surgical drill or a rotating cutting tool can cause damage to the cortical wall, especially along narrower portions of an IM canal and cortical wall.
Further, as cancellous bone is much weaker than cortical bone, conventional drilling instruments used in the IM canal have the potential to quickly drill through cancellous bone before unintentionally reaching the cortical wall and surrounding cortical bone. While one advantage of the above-described balloon compression devices is that the danger of damaging the cortical wall is minimal because cancellous bone is not cut, the above-described compression devices provide no means for forming larger cavities by cutting cancellous bone tissue safely without damaging the surrounding cortical wall. Further, the above-described balloon compression devices provide no means for removing cancellous bone tissue, which may be necessary for the formation of larger cavities within the IM canal.
In contrast, conventional drilling/reaming devices may be used to form the cavity. However, when using a conventional drilling/reaming device, the surgeon must be concerned with the pre-selected drill/reamer being too large for any part of the IM canal. If the drill/reamer is not properly selected, the cortical bone along an area where the cortical wall inner diameter is smaller than that of the drill/reamer may be unintentionally cut. Further, due to variations in the inner diameter of the cortical bone, the surgeon may be forced to select a drill bit or reamer size that is smaller than desired to avoid cutting cortical bone. As a result, the cavity may be smaller than desired.
Finally, another disadvantage to the prior art drilling/reaming devices is that an entry port for providing access to the IM canal must be axial with the IM canal. Typically, the entry port is drilled at the end of the bone through the joint. Often, this results in the removal of significant amounts of healthy cortical bone to reach the IM canal, and breaching an articular surface, which leads to joint pain. Further, if the fracture site is at an axial mid-point of the bone, more than half of the IM canal must be traversed to complete the procedure. Thus, it would be advantageous to provide a surgical instrument for forming cavities in IM canals that can utilize non-traditional entry port locations with an angled trajectory relative to the bone axis.
Accordingly, a need exists for an IM canal cavity forming device and method that can safely form cavities in IM canals without causing damage to cortical walls. There is also need for such devices that can remove cancellous bone tissue, marrow and other materials from the IM canal so that larger cavities can be formed. A need also exists for an IM canal cavity forming device that is of relatively simple construction and inexpensive to manufacture, that can be operated either manually or by a powered surgical drill, and that provides the surgeon with increased ability to create a cavity safely within the IM canal without damaging the surrounding healthy cortical bone. Further, it would be advantageous for such a device to be flexible and capable of entering the IM canal through an angled entry port, as opposed to an axial entry port at the end of the bone, i.e., through a joint.